From a commercial viewpoint, pepper is an important spice, for which its essential oil, responsible for the flavor, and its pungent principle, piperine, is sought.
More than 80 constituents have been identified in the essential oil of pepper. The main ones are 90 to 95% terpene hydrocarbons and the balance are oxygenated compounds.
The compounds of the essential oil therefore are mostly apolar. However, the great electronic density at the level of the double bonds--2 for monoterpenes, 3 for sesquiterpenes--favor interactions with electrophilic groups. Piperine exhibits a very slight basic character due to the presence of a disubstituted amide group, and comprises two conjugated double bonds.
Extraction of spices by a gas, under supercritical conditions, had already been proposed almost twenty years ago. Of these solvent gases under supercritical conditions were cited in patent GB No. 1,336,511 nitrous oxide, sulfur hexafluoride, fluoro hydrocarbons, ethane, ethylene or carbon dioxide.
The U.S. Pat. Nos. 4,123,559 and 4,490,398 describe processes for production of spices in two stages, using the gases cited above under supercritical conditions.
These extraction processes are performed under pressures of 300 to 350 bars.
More recently, the patent application EP No. 0.154.258 has as its object a process for the production of extracts of spices by extraction with a homogeneous mixture, in the supercritical state, consisting of a gaseous extraction agent, such as CO.sub.2, N.sub.2 O, ethane, propane, butane, ethylene, to which is added an organic solvent entraining agent. According to this technique, the extraction is performed at, at least 5 bars above the critical pressure of the gas and at about 1 to 60.degree. C. above the critical temperature of the gas.
A process has been sought making it possible to replace the toxic organic solvents used now for extraction of spices, especially pepper oleoresin (flavor+piperine), by a nontoxic liquid.
Further, a process has been sought making it possible to work at extraction pressures and temperatures lower than under supercritical conditions used in the prior art, cited above, to limit the investment costs of the high-pressure equipment. Reduction of the extraction pressure from 350 bars to 80 bars would reduce the costs of reactors under pressure by a factor of 2 to 3.